In order for this scenario to correctly predict galaxy properties, the baryons must retain a large fraction of their initial angular momentum.
However, early numerical simulations of galaxy formation contradicted this expectation [1]}, [2]}, [3]}. They found
a factor of \(\sim 30\)  loss of angular momentum for simulated galaxies, and referred to this as an “angular momentum catastrophe."
As simulations improved over the years, it became clear that much of this catastrophe was
actually a numerical artifact: too little resolution and too much numerical viscosity [4]}, [5]}, [6]}, [7]}, [8]}. Another possible contribution to solving the angular momentum problem may be through feedback effects which
can delay baryons from falling onto discs [9]}, [10]}, [11]}, [12]}.
With high numerical resolution and some feedback, galaxy simulations are now at a stage where angular momentum loss
may be a relatively minor problem. In this paper, we explore another option: that the discs of galaxies draw baryons
mainly from the inner parts of dark matter haloes. Some of the baryons in the outer parts may have not yet
collapsed onto the discs.
